(Appologies if this has already been asked!)

Are Aimpoints (or any other red dot sight) workable on a 20"?   I noticed that most of you put them on your M4.   If it is workable, what mounting do you suggest for a 20" flattop?

Actually, it should work slightly BETTER on a 20-incher, because with the added velocity the trajectory will be slightly flatter, thus bullet impact would be closer to line-of-sight over a greater distance than with a carbine. I'm a fan of ARMS for the QD throw-levers, but GG&G, and Knight's Armament also make some good mounts.

Thanks for the info.

What do you think of the "Rail Grabber" that S.W.F.A sells?

The cantilever mounts are ideal but they are not necessary.  The aimpoint railgrabber mount, mounted to the receiver, will work.  I have a railgrabber mounted to a receiver and while it may be a bit slower to engage, it still works pretty well for me.  The aimpoint mount is not as stout as the other mounts listed above, but it is reasonably stout and it will hold zero after being removed and reattached.  The US military, with the exception of some more advanced units that have discretionary funds, still uses railgrabber mounts for their aimpoints, and they seem to hold up for them.  At least I haven't heard of any problems arising from their use.

If money is an issue, the railgrabber will work, if you have the extra cash, you will most likely be happier with the ARMS mount with cantilever spacer.  I wouldn't bother looking at the KAC and GGG mounts, way too expensive, and have no real advantages over the ARMS unit to justify their higher cost.

FWIW, i have a reflex2 on my 20" A2 flat top and a telescoping stock. it's my M4-LB (long barrel)

i like the set up alot as i am a velocity nut on 5.56mm and it has less muzzel flash at night.

Thanks for the info.   Don't know, but what I may do is scope the 20" instead and save the Aimpoint for my M4.